The invention concerns a method for producing stemware, tumblers and the like hollow glassware by blow molding a molten solid gob of glass.
The invention is further directed to a device for producing stemware, tumblers and the like hollow glassware with a blow molding stage comprising a blow head with a blow work ring, a blowing unit, a mold, and a bottom plate in which a molten gob of glass can be shaped to form the desired hollow glass, and with devices containing a removal stage for removal of the hollow glassware from the blow molding stage and for delivery to subsequent processes.
In the known methods for producing the aforementioned molded hollow glass bodies, the starting glass is prepared in a glass-melting furnace operation or glass-melting tank operation. Accordingly, DE-A1-32 39 517 shows a method for producing goblet-type glass objects in which a glass gob delivered from the feeder of a glass melting furnace is placed on a press plunger and is pressed between this press plunger and a preform to form a glass tablet or pellet. The table which is still plasticized is then disengaged from the preform and placed on an annular body on which it sinks in a goblet-shaped manner at least in its middle portion through the influence of gravitational force. This tablet is then given its definitive shape in a mold.
A method of the type mentioned above requires a melt tank for removal of the glass gob for the hollow glasses to be molded. This glass tank operation and the subsequent hollow glassware production process are directly connected, so that the following kinds of interactions occur:
Inhomogeneous glass tank operation and glass tank charging, depending on the weight of the product.
It is necessary to adapt to the glass tank capacity when changing over production machinery (retooling or conversion), so that additional inhomogeneities occur in the melting process.
Since a glass tank feeds several production lines, only clear glass can be melted in the tank, and this clear glass can be colored in a costly, complicated process only immediately before being fed into the respective production machinery.
The product changeover period is dependent on the magnitude of the weight difference between the successive products because this has a considerable effect on the duration for changing over the feed devices into the new stable operating state.
With smaller batch sizes, there is an increase in the number of production changeovers, resulting in a corresponding reduction in production efficiency. In addition, modern production machinery, since it is conceived originally for large batches, requires extensive outlay on molds and tools for the respective product combined with a corresponding input of personnel and operating means.
Moreover, one result of the previous type of mechanical stemware production was a high proportion of remainder glass which can amount to as much as 50 percent by weight. This remainder glass (cullet) requires costly transporting devices and feed devices for purposes of remelting in the tank, where it occasions additional expending of heating energy.
The individual production machines of a production line are linked together in the known methods and devices and must consequently be adapted to one another. As the quantity of linked arrangements increases, so also does the breakage rate because there is a risk of breakage each time the glass is handled.
It is the object of the invention to carry out the method mentioned above and to construct the device mentioned above in such a way that a more economical production of the aforementioned hollow glassware is made possible. It will be possible to carry out the production of this hollow glassware independent from the tank operation glass melting process.
According to the invention, this object is met with respect to the method by the following steps:
production of solid glass blanks in the form of fabricated semifinished products in their own separate manufacturing line;
storage and supply of semifinished products;
feed of semifinished products from the reserve to the manufacturing line for shaping the hollow glassware accompanied by preheating of the semifinished products;
supplying preheated semifinished product for further heating;
heating of the semifinished product to blowing temperature to form a plastically deformable solid glass gob by additional heating;
mold blowing of the plasticized glass gobs to form hollow glass in a blow mold with support of the blown hollow glass body by a bottom lifter;
removal of the hollow glassware from the blow mold and delivery to subsequent processes. With respect to the device, the object is met by:
a stage with storage devices and transport devices for supplying and feeding intermediately stored solid semifinished glass products for the hollow glassware which is to be formed and which has been produced beforehand in its own separate device;
a subsequent preheating stage with heating devices for preheating the solid semifinished products;
a stage with transport devices for supplying the solid semifinished product to a semifinished product heating stage with heating devices for further heating of the semifinished products at least to a temperature close to the blowing temperature;
a transfer stage with devices for transferring the solid semifinished products that have been further heated in the semifinished product heating stage into the blow mold stage, where they are made available as plastically deformable solid glass gobs for blow molding the hollow glassware.
Since the glass raw material is in the form of semifinished product which is adapted to the end product and produced in stock in a separate process and is not heated to the necessary blowing temperature until immediately before the blowing process in a separate continuous furnace, a homogeneous glass tank operation with consistent melt quality is possible.
Simple conversion of the hollow glass fabrication from clear glass to colored glass is also possible.
The invention also advantageously results in a glass tank operation which is independent from the manufacturing line for the molded hollow glass body with respect to time, location and organization. The hollow glass manufacturing process can be carried out in a manageable, less cost-intensive environment, so that great flexibility is achieved in site selection. The high-technology, high-investment glass tank operation can also be carried out independent from and remote from the hollow glass manufacturing process.
As a result of the invention, the glass tank can also be used in a three-tiered manner without retooling interruptions for producing the semifinished products. This enables a more flexible manufacture of smaller batch sizes. It is also possible to test new techniques and/or technology at individual function modules of the device according to the invention without disrupting the entire production process. The invention also opens up possibilities for economizing on personnel, material, energy and mold costs.
There are a number of possibilities, some of which are shown hereinafter, for arranging and producing glass blanks in the form of fabricated semifinished products for mold blowing in their own separate manufacturing line.
According to a further development of the invention, a first possibility consists in producing semifinished product indirectly by punching (stamping) or cutting round flat glass disks from a flat glass as semifinished products for mold blowing.
This possibility has the following advantages:
simple manufacturing process, simple transport and simple supplying of semifinished products;
good, simple handling of the flat semifinished product;
splitting up of semifinished product production spatially into flat glass blank and the actual semifinished product production.
However, the following factors must be taken into account:
technological cost of semifinished product production;
the glass waste resulting from cutting out or punching out must be remelted;
the risk of destruction or damage to the semifinished product during transport.
According to a development of the invention, a further possibility consists in direct production of semifinished products by casting a flat tablet in a mold following the melting of a glass blank as semifinished product for mold blowing.
This second possibility has the following advantages:
simple manufacturing process (conventional tank operation glass melting process), simple transport and simple supply of cast semifinished products;
good, simple handling and supply of flat semifinished product.
However, the risk of destruction and damage to the semifinished product during transport must be taken into account.
A third possibility, according to a further development of the invention, consists in casting a profiled tablet whose shape is optimized with respect to the molded hollow glass body to be produced.
The advantages are:
simple manufacturing process for the shape-optimized, profiled tablet (conventional glass tank operation);
enables a process which is optimized for blowing.
The following considerations should be taken into account:
risk of destruction or damage to the semifinished product during transport;
difficult handling and storage of the profiled semifinished product.
A fourth possibility, according to a further development of the invention, consists in producing a shape-optimized semifinished product in a semifinished product carrier. This possibility is characterized by direct production of a semifinished product, whose shape is optimized with respect to the molded hollow glass body to be produced, by filling a semifinished product carrier having an optimized internal shape with glass raw material from a melt, wherein the semifinished product remains in the semifinished product carrier in the subsequent steps until the blown molded hollow glass body is severed and forms a processing unit together with this semifinished product carrier.
The semifinished product carrier is preferably a correspondingly shaped ring, wherein a receptacle for the semifinished product carrier is provided in the blowing unit of the blow molding stage as work ring during mold blowing.
This possibility has the following advantages:
protection of the semifinished product from destruction and damage by the surrounding semifinished product carrier;
enabling a process that is optimized for blowing, wherein wasted remainder glass can be reduced by up to 50% when the inner contour of the annular semifinished product carrier is optimal;
simple manufacturing process, simple transport automation and stackability of semifinished product;
facilitated handling processes through standardized geometric shape of the semifinished product carrier;
use of the ring as work ring during the blowing process;
substitute for excess or top glass, therefore less glass volume in circulation.
However, the following considerations must be taken into account:
supplying the semifinished product carrier;
need for process of severing the semifinished product from semifinished product carrier;
preparation and disposal of the semifinished product carrier.
In the production of molded hollow glass bodies in the shape of goblets with stems, there are different possibilities for assembling and connecting the stem and goblet. According to a first further development of the invention, the method is characterized by the assembling and connection of stems with the mold-blown goblet in the blow mold, wherein these stems are manufactured externally as semifinished product.
In a method of this kind, the stems are fabricated independent from the production of the hollow glass.
According to an alternative development of the invention, the method is characterized by the assembly and connection of stems with the mold-blown goblets in the blowing station, wherein the stems are manufactured within the manufacturing line.
In an embodiment form of the kind mentioned above, there is no longer a need to supply semifinished stem products and the substantial expenditure for feeding these semifinished products to the production process is eliminated.
The further heating of the semifinished product to blowing temperature can also be carried out in different ways. According to a first development of the invention, this further heating is carried out in two steps, namely, by a first further heating shortly before the blowing station, followed by transfer of the not-yet-plasticized semifinished product to this station, and by a second further heating of the semifinished product to blowing temperature in this station.
This embodiment form facilitates handling of the semifinished product in the blowing station.
According to an alterative embodiment form, it is also possible for the heating of the semifinished product to blowing temperature to be carried out in an individual step in a separate device with transfer of the plasticized semifinished product to the blowing station.
Since there are problems involved in the handling of plasticized glass, the transfer of the semifinished product to the blowing station in this alternative is also not without problems.
When the desired manufacturing depth provides for severing the top glass from the rest of the molded hollow glass bodies, this is preferably carried out by means of a laser beam in the blowing station after opening the mold.
When the method is carried out in this manner, further edge machining of the molded hollow glass body is dispensed with.
According to a further development of the invention, a semifinished product monitoring stage with devices for monitoring the state of the semifinished products is added between the supply stage and the preheating stage.
This ensures that only the semifinished products suitable for production will be supplied to the continued manufacturing process.
According to a further development of the invention, the heating devices in the preheating stage are formed by a continuous heating furnace with radiation burners or the like.
Conventional heating devices can accordingly be used in the preheating stage.
According to a further development of the invention, the transport devices in the stage for providing the semifinished products are formed by pushers in connection with a chute or by a gripper arm. In this way, it is possible to supply the semifinished products in a simple manner.
According to another development of the invention, the heating devices in the semifinished product heating stage are formed alternatively by a heat radiator, a gas radiator or gas-oxygen radiator or by microwave radiators which are arranged in a substantially closed chamber, preferably below the semifinished product.
This makes it possible to heat the core area of the glass blank while minimizing heat losses in a simple manner.
According to a development of the invention, the heating devices in the semifinished product heating stage are so arranged that the semifinished products are heated to a temperature in the neighborhood of the blowing temperature, preferably 900xc2x0 C., with heating to the blowing temperature in the blow head of the following blow molding stage through the use of a laser with beam feed through a bore hole in the blow head for supplying the compressed air.
This two-stage heating to blowing temperature has the advantage that the semifinished products are not plasticized until immediately before the blow molding stage and can also be handled more simply up to this stage.
As an alternative to this embodiment form, the heating devices can also be arranged in such a way that further heating to blowing temperature is carried out in an individual step in a separate device in parallel with the blowing process.
This variant has the advantage that it does not prolong the main cycle.
According to a development of the invention, the devices in the transfer stage are formed by a swivel arm with grippers. These devices allow a simple possibility for transferring the heated semifinished product to the blow mold stage.
In the known methods and devices, the individual process steps are carried out on a plurality of machines which are arranged one behind the other and spatially separated from one another. This conception is disadvantageous in that it is very personnel-intensive, causes relatively extensive glass breakage during transport from one machine to the other and requires relatively long conversion times of about 1.5 hours because the blowing machine and associated machinery must be set up for another product in a mutually dependent manner and production cannot begin again until the lengthy conversion process has been concluded; further disadvantages consist in the relatively high consumption of energy for glass melting because a relatively large amount of broken glass and top glass must be returned to the melt tank and remelted, and, not least, in the high mold costs resulting from the fact that a large quantity of mold sets must be kept in store irrespective of the batch size of the hollow glass article to be manufactured.
These disadvantages can be overcome, according to a further development of the invention, when the stages comprising semifinished product preparation, semifinished product heating, blow molding and removal are arranged as independent function modules and form the basic framework of a modular manufacturing unit to which further modules, such as stem feed, stem pressing, and severing of top glass, may be added optionally.
A particularly compact production device can be produced when a plurality of manufacturing units are combined in a modular manner to form a section and a plurality of sections are connected together to form a production device. Alternatively for this purpose, every manufacturing unit can be outfitted with individual function modules or a plurality of manufacturing units can share function modules. A clear material flow results when the stages comprising semifinished product supply, semifinished product monitoring and semifinished product preheating are arranged behind the manufacturing units and when a discharging device for joint discharge of the produced molded hollow glass bodies and an automatic mold changing device are provided transversely in front of the manufacturing units and longitudinal to the production device. In known cases, the molds were changed manually.
The modular production device characterized above has a number of advantages.
As a result of the increased automation when changing molds and by means of joining successive process steps on only one manufacturing device, it is possible to economize substantially on personnel.
Glass breakage is appreciably reduced because the transport paths between the process steps where waste currently takes place due to breakage are eliminated.
The modular construction of the manufacturing device in which every manufacturing unit operates autonomously has the following advantages when converting to a different product: Production can already take place at the manufacturing units that are converted first while additional stations are being converted (sectional production run). The changing of molds necessitated in the process is carried out automatically. Production losses due to conversion work are noticeably reduced compared with methods according to prior art because of these reduced conversion periods in the installation according to the invention.
Through improved utilization of the raw glass, energy consumption for melting glass can be reduced because less broken glass and top glass is returned to the melt tank.
In the production device according to the invention, the quantity of molds can be adapted to the batch size of the hollow glass article to be produced because also different molds can be used simultaneously on the modular manufacturing units. Moreover, in the case of mold sets of lower piece number, fewer molds need to be kept in store as substitutes. For example, in the manufacture of goblets with stems, the quantity of molds can be adapted to the batch size by stem fabrication which is independent from the blowing process, irrespective of the goblet which is to be added later. Accordingly, stems which will subsequently be combined with different goblets to form stemware can be manufactured in high piece numbers because different goblet shapes can have the same stem geometries in a series of glasses. This results in optimum utilization of molds which improves with increasing batch sizes. Further, the maintenance intervals can be prolonged appreciably.
Therefore, considerable economies can be achieved by means of this concept in the area of press molding and blow molding.
Further developments and advantages of the invention are given with reference to the description of embodiment examples shown in the drawings.